1. Field of the Invention
The present invention relates to a noise prevention high voltage resistance wire, and more specifically to an ignition cord used for an automotive vehicle.
2. Description of the Prior Art
Wires such that a non-metallic conductive wire is covered by insulation material have conventionally been used as noise prevention high voltage resistance wires for automotive vehicle ignition cords.
These non-metallic conductor wires are manufactured by applying or extruding a conductive composite around a heat-resistance reinforcing core-wire such as glass fiber or aromatic polyamide fiber, and the conductive composite is manufactured by mixing conductive carbon material such as graphite powder or conductive carbon block with heat resistance rubber or plastic.
In these prior-art non-metallic conductors, however, there exists a problem such that the electric resistance changes markedly according to change in temperature. To overcome this problem, some attempts that carbon fiber is used as the conductive carbon material have so far been made.
An example of these attempts is disclosed in Japanese Published Unexamined Patent Appl. No. 55-122308, in which carbon fiber is combined with carbon particle (e.g. carbon black) or graphite particle. This carbon fiber used as conductive material should be cut off or pulverized to a several millimeter or one millimeter length (in some cases) so as to be uniformly mixed with silicon rubber or fluorine rubber.
In the prior-art conductive material based upon pulverized pitch carbon fiber, however, there exist other problems in that a sufficient conductivity cannot be obtained unless a great quantity of graphite of a high graphitization is mixed and further where a great quantity of graphite is mixed, the processability or workability of the combined composite is degraded and additionally the resistance value is scattered, thus resulting in a difficulty in manufacturing a uniform resistance wire.
On the other hand, in the case of carbonized synthetic fiber (e.g. PAN carbon fiber), since fine split or nap is readily produced and the length of the fiber is different when the fiber is pulverized, there still exist problems in that the processability of the combined conductive composite is not excellent and also the conductivity is dispersed. To prevent fiber nap produced when the fiber is pulverized and to improve the processability, the carbon fiber is often processed by various organic agents (e.g. a surface active agent, a high molecular substance, etc.). However, this processing will exert a harmful influence upon the conductivity characteristics of the wire.
In summary, non-metallic conductor made of conductive composite including carbon fiber involves various problems such that the processability is not good; the characteristics are not uniform; the resistance is not stable against temperature change; and the conductivity is not stable against internal stress change due to an external force such as bending.